The present invention relates to a gas detecting device for detecting a gas in an atmosphere. More particularly, the invention relates to a gas detecting device which is suitable for using as a gas alarm for leak of a city gas or a liquefied petroleum (LP) gas.
The present invention also relates to a gas detecting device which discriminates a gas from an atmosphere including a plurality of different kind of gases.
Generally, a gas detecting device is responsive to various kind of gases such as isobutane, propane, ethane, methane, ethanol, propylene, toluene, xylene, methanol, hydrogen, carbon monoxide, etc. Therefore, when a specified gas is to be detected, the gas detecting device generates a noise signal in response to another gas mixed in the atmosphere. For example, with regard to a household gas detector (gas alarm), it is desirable that the detector is sensitive only to a methane gas when a city gas is used. However, the gas detector which is usually disposed on a ceiling is sensitive to the water vapor or an alcohol gas which is often generated in a domestic kitchen.
Therefore, in order to selectively detect a specified gas, the conventional gas detecting device is constructed in such a way that it comprises a filter means for selecting the specified gas or that the functional temperature thereof is arranged so that the detector becomes most sensitive to the specified gas. However, such a way for selectively detecting a gas is undesirable from an aspect of cost as well as reliability of detection of the specified gas.
There are two types of the gas detecting device. One is a semiconductor detection type using a metallic oxide and the other is a contact combustion type using a catalyst. Either of the two types has to heat a gas sensitive element by using a heater means, which consumes a relatively large power. Besides, the conventional gas decting device is not fully and accurately responsive to the gas.
In order to save the power consumption and improve the responsiveness of the detector, a gas detecting device is proposed in Japanese Patent Application Laying Open (KOKAI) No. 61-191953 wherein a minutely processed fine microheater of Japanese Patent Publication (KOKOKU) No. 62-2438 is used. The proposed gas detector is improved in the points of power consumption and responsiveness to the gas. However, the proposed gas detector is economically still undesirable since it requires a filter to select a gas. Also, the filter is for selecting one specified gas from a mixed gas atmosphere excluding other gases. Therefore, the conventional gas detector using the filter is not capable of discriminating a plurality of gases by itself.